主席樹——模板整理__資料結構

函數式線段樹。
利用了可持久化的思想，降低時間和空間複雜度。

#include<cstdio>#include<cstring>#include<algorithm>using namespace std;const int maxn=2000005;int n,Q,a[maxn],b[maxn];struct node{    int L,R,sum;    node* ch[2];    void maintain(){ sum=ch[0]->sum+ch[1]->sum; }} *rt[maxn], base[maxn], *len=base, nil, *null=&nil;node* newnode(int L,int R,int sum){    len->L=L; len->R=R; len->sum=sum;     len->ch[0]=len->ch[1]=null;    return len++;}node* build(int L,int R){    node* p=newnode(L,R,0);    if(L==R) return p;    int mid=(L+R)>>1;    p->ch[0]=build(L,mid); p->ch[1]=build(mid+1,R);    p->maintain(); return p;}node* Updata(node* pre,int val){    node* p=newnode(pre->L,pre->R,pre->sum);     p->ch[0]=pre->ch[0]; p->ch[1]=pre->ch[1];    if(p->L==p->R){        p->sum++; return p;    }    int mid=(p->L+p->R)>>1;    if(val<=mid) p->ch[0]=Updata(p->ch[0],val);            else p->ch[1]=Updata(p->ch[1],val);    p->maintain(); return p;}int Query(node* tl,node* tr,int K){    if(tl->L==tl->R) return b[tl->L];    int tem=tr->ch[0]->sum-tl->ch[0]->sum;    if(K<=tem) return Query(tl->ch[0],tr->ch[0],K);    return Query(tl->ch[1],tr->ch[1],K-tem);}int find(int x){ return lower_bound(b+1,b+1+b[0],x)-b; }int main(){    freopen("poj2104.in","r",stdin);    freopen("poj2104.out","w",stdout);    scanf("%d%d",&n,&Q);    for(int i=1;i<=n;i++) scanf("%d",&a[i]), b[++b[0]]=a[i];    sort(b+1,b+1+b[0]);    b[0]=unique(b+1,b+1+b[0])-(b+1);    rt[0]=build(1,b[0]);    for(int i=1;i<=n;i++) rt[i]=Updata(rt[i-1],find(a[i]));    while(Q--){        int x,y,z; scanf("%d%d%d",&x,&y,&z);        printf("%d\n",Query(rt[x-1],rt[y],z));    }    return 0;}